1. Field of the Invention
This invention relates to improvements in respirators and has particular reference to means and method for indicating end-of-service life of respirator cartridges.
2. Discussion of the Prior Art
Respirator cartridges for filtration against vapors or gases are generally filled with adsorbent solids which are able to trap the vapors or gases on their surfaces and cellular interstices. When exposed to adsorbing vapors and gases over a period of time, the available surfaces and interstices of the absorbing solid eventually become filled up and no further adsorption can occur. When this happens to the adsorbent within a respirator cartridge, the cartridge is no longer effective as a filtering device and consequently offers no protection to the respirator wearer.
Because of this danger to the wearer, the use of prior art air purifying respirators for protection against air contaminants having poor warning properties is not recommended. A contaminant has poor warning properties if its odor, taste, or irritation threshold level is greater than the permissable exposure limits, or if there is insufficient toxicological data to determine an exposure limit. Exposure limits for most gases are published regularly by the "American Conference of Governmental Industrial Hygienists".
In many industries, prior art air purifying respirators are used for substances having poor warning properties by implementing special work practices involving determination of the ambient level of the air contaminant and using a respirator cartridge for only a period of time when the protection level that it offers is sufficient to protect the wearer from the hazard at its ambient concentration. Administrative control of chemical vapor respirator cartridge service life is, however, tedious, costly and complex with less than optimum reliability. The U.S. National Institute for Occupational Safety and Health (NIOSH) does not recommend administrative control of respirator cartridge service life and has suggested that when substances with poor warning properties are encountered in the workplace at concentration levels above the permissible exposure limits, other forms of respirators such as air supplied devices be used or that air purifying respirators be equipped with systems which can be relied upon to indicate when they are no longer filtering effectively.
In attempts to accomplish the latter, the prior art includes respirator canisters having windows for detecting change of color of the canister adsorbent or impregnated indicator strips e.g. as in U.S. Pat. No. 1,537,519. Another system for detecting exhaustion of a respirator for protection against carbon monoxide includes a reagent which, on contact with carbon monoxide, will generate a vapor causing irritation of the eyes, nose and/or throat of the wearer as a warning of respirator exhaustion. U.S. Pat. No. 1,414,194 is exemplary. Also well known is an arrangement for detecting carbon monoxide utilizing a material called Hopcalite which interacts with carbon monoxide to produce carbon dioxide and heat. The carbon dioxide is then utilized to produce a color change in an adsorbent which indicates the original presence of carbon monoxide.
Chemically treated filters can provide color indication of moisture content of air discharged from the filter as in U.S. Pat. No. 2,528,539, for example, and electrolytic oxygen sensors in rebreathing apparatuses have been used, e.g. as in U.S. Pat. No. 3,695,261 to operate exhaust valves, warning lights or meters.
Carbon dioxide adsorbing apparatuses applied to patients undergoing anesthesia are also well known in the art. These apparatuses may embody indicator agents which change color in the course of absorption and depletion of the absorbtive capacity of the devices.
While the aforesaid various forms of prior art respirator cartridge residual life or exhaustion indication and/or breathing control systems may in some cases serve their respective purposes very well, those intended for protection against toxic vapors and gases having poor warning properties generally fall short of meeting present day requirements in a manner of readily acceptable efficiency.
It having been discovered according to this invention that the exothermic process between a respirator adsorbent and the adsorbate (vapors or gas adsorbed) may be utilized in end-of-service life detection rather than the approaches of the prior art, a principal object of the invention is to provide for reliable vapor-gas respirator cartridge end-of-service life indication utilizing the aforesaid exothermic process and to provide for reliable visual or audio warning of cartridge failure, i.e. failure to provide respirator protection at or above a hazard concentration level that is considered safe to inhale.
More particularly, it is another object of the invention to provide for positive indication of cartridge exhaustion independently of a user's physical senses of taste, smell or sensation of irritation and further independently of environmental organic vapor or gas concentrations and variations thereof in the course of respirator use.
Other objects and advantages of the invention will become apparent from the following description.